The measurement of lung volumes using body plethysmography and helium dilution methods in COPD patients: a correlation and diagnosis analysis

Chronic obstructive pulmonary disease (COPD) is a chronic airway disease characterized by persistent airflow limitation. Moreover, lung hyperinflation evaluated by lung volumes is also the key pathophysiologic process during COPD progression. Nevertheless, there is still no preferred method to evaluate lung volumes. For this study, we recruited 170 patients with stable COPD to assess lung volumes stratified by airflow limitation severity. Lung volumes including residual volume (RV) and total lung capacity (TLC) were determined by both body plethysmography and helium dilution methods. The discrepancies between these two methods were recorded as ΔRV%pred, ΔTLC%pred, and ΔRV/TLC. We found that ΔRV%pred, ΔTLC%pred, and ΔRV/TLC increased significantly with the severity of COPD. The differences of lung capacity between these two methods were negatively correlated with FEV1%pred, and diffusing capacity for carbon monoxide (DLCO%pred). Moreover, the receiver operating characteristic (ROC) for ΔTLC%pred to distinguish severe COPD from non-severe COPD had an area under curve (AUC) of 0.886. The differences of lung volume parameters measured by body plethysmography and helium dilution methods were associated with airflow limitation and can effectively differentiate COPD severity, which may be a supportive method to assess the lung function of stable COPD patients.